1. Field of the Invention
This invention relates to gas turbine engine control systems and more particularly to an apparatus in a gas turbine control system for detecting the failure of an engine parameter sensor and taking corrective action.
2. Description of the Prior Art
Gas turbine engine control systems, particularly for use in controlling aircraft engines, generally include a number of sensors which measure various engine parameters. These sensors measure performance parameters, typically gas generator and fan rotational velocities and engine operating pressures and temperatures as well as controlled parameters, typically fuel flow and variable geometry positions. The signals developed by such sensors are used to control actuators such as of the electrohydraulic and electromechanical type which vary the position of the controlled parameters, to control the operation of the engine. In a conventional engine control system the engine parameter sensors are connected directly to a control computational unit within the engine control system. The control computational unit may be analog in which dedicated circuits perform continuous computations or it may be digital in which computations are performed sequentially on a time-sharing basis. In either case, the control computational unit using directly the sensed values for both the engine performance parameters and the controlled parameters and known engine behavior characteristics computes signals to modify the controlled parameters in order to maintain a selected level of engine performance. The signals from the control computation unit are amplified, conditioned and then transmitted to the actuators which alter the controlled parameters.
One potential problem associated with such prior art control systems is that the loss of a signal representative of the true value of the parameter from one or more engine performance parameter sensors or controlled parameter sensors may cause a loss of control of one or more of the controlled parameters resulting in a loss of control of engine performance. Such a signal loss may be due to any number of factors including the failure or malfunctioning of the sensor itself, the failure or malfunctioning of the interconnection between the sensor and the control computational unit or the failure of malfunctioning of any of the processing circuitry for the sensor signals. All such failures, abnormal operations, malfunctions, etc. sometimes are referred to herein as failure or failures.
Accordingly, it is the primary object of this invention to provide a control system for a gas turbine engine which prevents loss of control of engine performance in the event of the loss of a true signal from an engine parameter sensor.
It is a further object of this invention to provide such a control system which transmits an indication to the engine operator when the failure or malfunctioning of an engine parameter sensor or its associated circuitry has occurred.